Name: gas cooling and heating in throttling
Uploaded: 2025-05-22T09:05:59.000Z
Duration: 1 min 21 s
Channel: JoVE

K12 Standards

Florida Department of Education

High School

Physical Science

SC.912.P.10

SC.912.P.10.2

Joule-Thomson Effect

L'effetto Joule-Thomson dimostra che in un sistema adiabatico, se un gas mantenuto ad alta pressione è costretto a passare attraverso un tappo poroso in una regione di bassa pressione, si espande e occupa un volume maggiore, cambiando la sua temperatura e, di conseguenza, la sua energia interna.
In questo processo adiabatico, la variazione dell'energia interna del gas deve essere uguale al lavoro svolto sul gas meno il lavoro svolto dal gas. Riorganizzando i termini, si nota che l'entalpia è conservata.
La variazione di temperatura con pressione a entalpia costante è definita come coefficiente di Joule-Thomson. Utilizzando il teorema di reciprocità e sostituendo la relazione di capacità termica, il coefficiente di Joule-Thomson è espresso in termini della derivata parziale dell'entalpia con la pressione.
Esprimendo la derivata parziale in termini di entropia e usando la relazione di Maxwell si ottiene il coefficiente di Joule-Thomson in funzione della temperatura.
Un valore positivo del coefficiente indica il raffreddamento, mentre un valore negativo indica il riscaldamento del gas durante l'espansione.
Per un gas ideale, il coefficiente di Joule-Thomson è zero poiché la sua temperatura rimane la stessa quando passa alla regione di bassa pressione.

<ol>
	<li>Blundell, S.J. e Blundell, K.M. (2010). Concetti di Fisica Termica. Seconda edizione. New York, Stati Uniti: Oxford University Press. pp. 316.</li>
	<li>Rex, A (2017). La fisica termica di Finn. Terza edizione. Boca Raton, FL: CRC Press. Pagine 212.</li>
</ol>

effetto joule-thomson

L'effetto Joule-Thomson, noto anche come effetto Joule-Kelvin, descrive la variazione di temperatura di un fluido quando viene costretto attraverso una valvola o un tampone poroso mantenendolo in un ambiente termicamente isolato. Questo esperimento è chiamato processo di throttling ed è un effetto importante ampiamente utilizzato nella refrigerazione e nella liquefazione dei gas.

In questo esperimento, un gas ad alta pressione viene forzato attraverso una valvola di regolazione o un tampone poroso verso una regione a pressione inferiore. Il gas si espande mentre passa nella regione a bassa pressione e occupa un volume maggiore rispetto al volume iniziale. Viene svolto lavoro sul gas quando viene forzato attraverso una valvola di regolazione. Tuttavia, quando si espande, il gas svolge lavoro sui dintorni. La temperatura del gas varia in questo processo; quindi, raggiunge una nuova energia interna. La variazione dell'energia interna del gas deve essere uguale al lavoro svolto sul gas meno il lavoro svolto dal gas. Si è scoperto che l'entalpia è conservata (isentalpica) in questo processo di flusso.

La variazione di temperatura del gas quando la pressione viene ridotta a entalpia costante è data dal coefficiente di Joule-Thomson:

<img alt="Equation1" src="/files/ftp_upload/14174/14174_Equation_1.png" style="text-align: center; height: 42px;" />

Poiché la temperatura del gas varia, il coefficiente di Joule-Thomson può assumere segni diversi, a seconda che il gas si riscaldi o si raffreddi. La curva di inversione nel piano T-p spiega il riscaldamento e il raffreddamento del gas durante il processo di throttling.

<img alt="Figure1" src="/files/ftp_upload/14174/14174_Figure_1.png" />

La curva di inversione separa la regione di riscaldamento dalla regione di raffreddamento. I massimi delle diverse isentalpe giacciono sulla curva di inversione. Si noti che un'isentalpa è la traiettoria dei punti finali dei diversi processi di throttling, partendo dallo stesso stato iniziale. A seconda di dove vengono scelti i punti iniziali e finali, durante il processo di throttling possono essere prodotti effetti sia di riscaldamento che di raffreddamento.

Il coefficiente di Joule-Thomson è zero per un gas ideale, indicando che non c'è variazione di temperatura quando un gas ideale subisce un processo di throttling. Il coefficiente è negativo per i gas reali a temperature estremamente alte e estremamente basse.

Effetto Joule-Thomson

L'effetto Joule-Thomson, noto anche come effetto Joule-Kelvin, descrive la variazione di temperatura di un fluido quando viene forzato attraverso una valvola o ...

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gas cooling and heating in throttling

Gas cooling and heating in throttling is explained by the Joule-Thomson effect, also called the Joule-Kelvin effect. It describes how a fluid changes temperature when it passes through a valve or porous plug in a thermally insulated system. This type of flow is called a throttling process.

In the experiment, a high-pressure gas is forced through a throttle valve or porous plug into a lower-pressure region. The gas expands as it moves into the larger volume. Work is done on the gas as it is pushed through the valve. After expansion, the gas also does work on the surroundings.

Because the temperature changes during the process, the gas reaches a new internal energy state. The change in internal energy equals the work done on the gas minus the work done by the gas. In this flow process, enthalpy stays constant, so the process is isenthalpic. The Joule-Thomson coefficient gives the temperature change when pressure drops at constant enthalpy.

The gas may either warm up or cool down, so the Joule-Thomson coefficient can be positive or negative. The inversion curve on a temperature-pressure diagram shows where heating changes to cooling. It separates the heating region from the cooling region, and the peaks of different isenthalps lie on this curve. An isenthalp is the set of end points for throttling processes that start from the same initial state.

Depending on the starting and ending points, throttling can produce either heating or cooling. For an ideal gas, the Joule-Thomson coefficient is zero, so no temperature change occurs during throttling. For real gases, the coefficient is negative at extremely high and extremely low temperatures. This effect is important in refrigeration and in the liquefaction of gases.

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Gas cooling and heating in throttling is explained by the Joule-Thomson effect, also called the Joule-Kelvin effect. It describes how a fluid changes temperature when it passes through a valve or porous plug in a thermally insulated system. This type of flow is called a throttling process. In the experiment, a high-pressure gas is forced through a throttle valve or porous plug into a lower-pressure region. The gas expands as it moves into the larger volume. Work is done on the gas as it is...

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Gas Cooling and Heating in Throttling

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